The overall aim of this proposal is to further develop our model for B cell activation and proliferation that employs in vitro infection by Epstein-Barr virus. These studies will provide a better understanding of this mechanism of normal and neoplastic B cell growth in vitro and in vivo and on the mechanisms by which EBV sustains a latent infection. The proposal focuses on three membrane proteins whose expression is closely associated with the proliferation of EBV infected B cells. 1) BLAST-1 - a panel of monoclonal antibodies will be raised to BLAST-1 and used to analyze the role of this molecule in proliferation and cell interaction. 2) CD23/BLAST-2 - the end shed form of CD23/BLAST-2 (25 kd chain) is associated with a 12 kd chain of unknown origin. We will analyze the role of this chain in the autocrine growth of B lymphoblasts that is driven by S-BLAST-2. Specific antibody reagents and a cDNA clone will be derived for this purpose using the purified 12 kd protein. 3) p63/LMP - the sites of phosphorylation and specific cleavage of the pp29 subfragment will be identified by purification and specific chemical cleavage and sequencing of pp29. This will then allow the specific mutation of these sites in order to study their role in the function of p63/LMP.